<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<style type="text/css">
			
			#big_div{
				width: 500x;
				text-align: center;
			}
			.dingbu{
				background-color: blue;
				height: 40px;
			}
			.caidan{
				background-color: green;
				height: 20px;
			}
			.div1{
				float: left;
				background-color: gainsboro;
				margin: 0px 5px 0px 10px;
				width: 150px;height: 50px;
			}
			.div2{
			    float: left;
				background-color: red;
				margin: 0px 5px 0px 10px;
				width: 150px;height: 50px;

			}.div3{
			    float: left;
				background-color: orange;
				margin: 0px 5px 0px 10px;
				width: 150px;height: 50px;
				
			}
			.bottom{
				background-color: blueviolet;
				clear: both;
			}
		</style>
	</head>
	<body>
		<div id="big_div">
			<div class="dingbu">顶部</div>
			<div class="caidan">菜单</div>
			<div class="float">
				<div class="div1">内容1</div>
				<div class="div2">内容2</div>
				<div class="div3">内容3</div>					
			</div>
			<div class="bottom">联系我们</div>
		</div>
	</body>
</html>